Many structures in display substrates, integrated circuits and the like are all prepared by a photo-lithography process, and exposure is an important step in the photo-lithography process, which is performed mainly by a mask plate.
As shown in FIG. 1, a mask plate includes a light blocking region 12 and a light transmitting region 11, wherein the light blocking region 12 can block light and the light transmitting region 11 allows light to transmit therethrough. Therefore, exposure light (for example ultraviolet light) radiated to the mask plate vertically can only transmit through the light transmitting region 11 so as to expose a region corresponding to the light transmitting region 11, to form a corresponding exposure pattern on the region.
As the technology develops, some structures in display substrates, integrated circuits and the like are becoming finer, and the corresponding size of the light transmitting region 11 is becoming smaller as well. Thus, as shown in FIG. 1, light passing through the light transmitting region 11 is equivalent to it passing through a fine slit, there inevitably occurs a significant diffraction and thus an oblique radiation is generated, further resulting in a larger width of a region actually illuminated by the light than a width of the light transmitting region 11, which affects a precision of the exposure and a resolution.